PublicKey (Javadocs [I2P+ 2.13.0+] - API Version 0.9.70+)

java.lang.Object
- net.i2p.data.SimpleDataStructure
- - net.i2p.data.PublicKey

All Implemented Interfaces:
DataStructure
Direct Known Subclasses:
NextSessionKey
```
public class PublicKey
extends SimpleDataStructure
```
Cryptographic public key for asymmetric encryption in I2P.
PublicKey provides the encryption component of I2P's asymmetric cryptography:
- Default Algorithm: ElGamal 2048-bit (256 bytes)
- Modern Support: Variable length and type support since 0.9.38
- Key Structure: Contains only public exponent
- Constants: Prime numbers defined in crypto specification
Supported Algorithms:
- ElGamal 2048: Legacy algorithm, 256-byte keys
- ECIES X25519: Modern elliptic curve, 32-byte keys
- Unknown Types: Forward-compatible support for future algorithms
Key Format:
- ElGamal: 256-byte public exponent only
- Elliptic Curve: Variable length based on curve parameters
- Type Encoding: Algorithm type stored with key data
- Validation: Length and format checking per algorithm
Usage:
- Encryption: Encrypt messages for corresponding PrivateKey
- Key Exchange: Participate in ElGamal key exchange
- Identity: Part of Destination cryptographic identity
- Verification: Public key validation and distribution
Performance Features:
- LRU Caching: Frequently used keys cached for efficiency
- Factory Methods: Static creation methods for cache access
- Efficient Storage: Optimized byte representation
- Fast Comparison: Optimized equals() and hashCode()
Security Considerations:
- Algorithm Choice: Prefer modern algorithms (X25519)
- Key Validation: Verify key parameters before use
- Key Distribution: Safely transmit public keys
- Size Limits: Currently limited to 256 bytes maximum
Migration Path:
- Legacy: ElGamal 2048-bit for backward compatibility
- Modern: ECIES X25519 for better performance
- Future: Extensible design for new algorithms
Implementation Notes:
- Size Limitation: Support for keys >256 bytes not yet implemented
- Cache Index: First 4 bytes used for LRU cache lookup
- Type Safety: Algorithm type validation on creation
Thread Safety:
- Immutable Data: Key data cannot be modified after creation
- Thread-Safe Cache: Static factory methods are thread-safe
- Safe Sharing: Instances can be safely shared between threads

Field Summary
Fields
Modifier and Type Field and Description
static int KEYSIZE_BYTES
Default key size in bytes (256 for ElGamal).
- Fields inherited from class net.i2p.data.SimpleDataStructure
  _data

Fields
Modifier and Type	Field and Description
`static int`	`KEYSIZE_BYTES` Default key size in bytes (256 for ElGamal).

Constructor Summary

Constructors
Constructor and Description
`PublicKey()` Creates a new PublicKey with the default ElGamal type.
`PublicKey(byte[] data)` Construct from raw key data.
`PublicKey(EncType type)` Construct a new public key.
`PublicKey(EncType type, byte[] data)` Construct a new public key.
`PublicKey(int typeCode, byte[] data)` Unknown type only.
`PublicKey(String base64Data)` Constructs from base64.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`static void`	`clearCache()` Clears the public key cache.
`static PublicKey`	`create(byte[] data, int off)` Pull from cache or return new.
`static PublicKey`	`create(InputStream in)` Pull from cache or return new.
`boolean`	`equals(Object obj)` Compares this public key with another object for equality.
`byte[]`	`getPadding(KeyCertificate kcert)` Get the portion of this (type 0) PK that is really padding based on the Key Cert type given, if any
`EncType`	`getType()` Gets the encryption type of this public key.
`int`	`getUnknownTypeCode()` Gets the type code for unknown encryption types.
`int`	`hashCode()` Hash code combining the type and data.
`int`	`length()` Key length in bytes, determined by the encryption type.
`String`	`toString()` String representation showing type and data size.
`(package private) PublicKey`	`toTypedKey(KeyCertificate kcert)` Up-convert this from an untyped (type 0) PK to a typed PK based on the Key Cert given.

Methods inherited from class net.i2p.data.SimpleDataStructure
calculateHash, fromBase64, fromByteArray, getData, read, readBytes, setData, toBase64, toByteArray, writeBytes

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Field Detail
  - KEYSIZE_BYTES
```
public static final int KEYSIZE_BYTES
```
    Default key size in bytes (256 for ElGamal).
- Constructor Detail
  - PublicKey
```
public PublicKey()
```
    Creates a new PublicKey with the default ElGamal type.
  - PublicKey
```
public PublicKey(byte[] data)
```
    Construct from raw key data.
    Parameters:
    data - must be non-null
  - PublicKey
```
public PublicKey(EncType type)
```
    Construct a new public key.
    Parameters:
    type - if null, type is unknown
  - PublicKey
```
public PublicKey(EncType type,
                 byte[] data)
```
    Construct a new public key.
    Parameters:
    type - if null, type is unknown
    data - must be non-null
  - PublicKey
```
public PublicKey(int typeCode,
                 byte[] data)
```
    Unknown type only.
    Parameters:
    typeCode - must not match a known type. 1-255
    data - must be non-null
  - PublicKey
```
public PublicKey(String base64Data)
          throws DataFormatException
```
    Constructs from base64. ElGamal only.
    Parameters:
    base64Data - a string of base64 data (the output of .toBase64() called on a prior instance of PublicKey
    Throws:
    DataFormatException - if the data is malformed
- Method Detail
  - clearCache
```
public static void clearCache()
```
    Clears the public key cache.
  - create
```
public static PublicKey create(byte[] data,
                               int off)
```
    Pull from cache or return new. ELGAMAL_2048 only! Deprecated - used only by deprecated Destination.readBytes(data, off)
    Parameters:
    data - the data to decrypt
    off - the offset into the data
    Returns:
    the result
  - create
```
public static PublicKey create(InputStream in)
                        throws IOException
```
    Pull from cache or return new. ELGAMAL_2048 only!
    Parameters:
    in - the input stream
    Returns:
    the result
    Throws:
    IOException - if an I/O error occurs
  - equals
```
public boolean equals(Object obj)
```
    Compares this public key with another object for equality.
    Overrides:
    equals in class SimpleDataStructure
    Parameters:
    obj - the object to compare
    Returns:
    true if equal
  - getPadding
```
public byte[] getPadding(KeyCertificate kcert)
```
    Get the portion of this (type 0) PK that is really padding based on the Key Cert type given, if any
    Parameters:
    kcert - the key certificate
    Returns:
    trailing padding length > 0 or null if no padding or type is unknown
    Throws:
    IllegalArgumentException - if this is already typed to a different type
  - getType
```
public EncType getType()
```
    Gets the encryption type of this public key.
    Returns:
    null if unknown
  - getUnknownTypeCode
```
public int getUnknownTypeCode()
```
    Gets the type code for unknown encryption types. Only valid if getType() returns null
    Returns:
    the unknown type code
  - hashCode
```
public int hashCode()
```
    Hash code combining the type and data.
    Overrides:
    hashCode in class SimpleDataStructure
    Returns:
    the hash code
  - length
```
public int length()
```
    Key length in bytes, determined by the encryption type.
    Specified by:
    length in class SimpleDataStructure
    Returns:
    the legal length of the byte array
  - toString
```
public String toString()
```
    String representation showing type and data size.
    Overrides:
    toString in class SimpleDataStructure
  - toTypedKey
```
PublicKey toTypedKey(KeyCertificate kcert)
```
    Up-convert this from an untyped (type 0) PK to a typed PK based on the Key Cert given. The type of the returned key will be null if the kcert sigtype is null.
    Parameters:
    kcert - the key certificate
    Returns:
    the typed public key
    Throws:
    IllegalArgumentException - if this is already typed to a different type

Class PublicKey

Field Summary

Fields inherited from class net.i2p.data.SimpleDataStructure

Constructor Summary

Method Summary

Methods inherited from class net.i2p.data.SimpleDataStructure

Methods inherited from class java.lang.Object

Field Detail

KEYSIZE_BYTES

Constructor Detail

PublicKey

PublicKey

PublicKey

PublicKey

PublicKey

PublicKey

Method Detail

clearCache

create

create

equals

getPadding

getType

getUnknownTypeCode

hashCode

length

toString

toTypedKey